In contrast with the digital photography, film photography traditionally has an exposure tolerance of two to four stops. An original scene exposed within this tolerance range will retain a good quality tonal curve due to the film, which is the recording medium, having a light sensitivity range which exceeds the tonal extremes in an average scene of two to four stops. Exposure for digital photography has a very narrow range, so that when there is over exposure or under exposure, part of the information is lost. Consequently, unless you initially achieve the desired exposure you make an inferior image file, which will not be in full detail either in highlight areas or shadow areas. There is no way to retrieve these lost details for the image file. Consequently, in digital photography techniques have evolved to fix images after they have been taken. This is a time consuming and relatively expensive undertaking in which it is still very difficult to compensate for information missing from an image.
Inside digital cameras there is a sensor on which a latent light impression of an original scene is made. Based on latent information from the sensor, a central processing unit in the camera processes the information into a proper color spectrum and into a proper color curve that retains the detail from highlight to shadow. The quality of image produced using the latent light impression frequently has diminished quality due to exposure error.
All sensors inside cameras have an optimal sensitivity setting (ISO), whether it is due to the sensitivity of film or to the sensitivity of image sensors in digital cameras. Sensitivity has an optimal range where it produces the absolute best image file in terms of color fidelity with the least image defects. In producing an optimal image file, the image file will be given a rated ISO, e.g., 100. Digital cameras have the capability of shooting other ISOs, but as one deviates from the optimum image quality suffers. When deviating from the optimal ISO, noise is introduced into the image files from the CPU and arbitrary abnormalities known as artifacts become visually apparent and the quality and color degrade. Thus, producing optimal digital image files is difficult for the professional photographer and extremely difficult for the consuming public.
Hand held light meters do not adequately compensate for inaccuracies in exposure because tolerances are typically plus or minus a half stop of exposure. Typically light meters select a middle tone, the placement of which varies from one manufacturer to another. Since light meters peg the middle of the tonal curve, light meters select gray rather than the black and white extremes. Pegging the middle of the tonal curve can result in the photographer loosing information at one or the other extreme so that light metering does not work effectively. This forces camera manufactures to develop methods to fix latent information. In order to compensate for inadequate latent information, camera manufacturers provide you with software solutions for manipulating improperly exposed and color-balanced images. But, these “back end fixes” almost invariably produce inferior image files with which before you can even start to produce a print, require very labor intensive efforts having three times the amount of work to process an image file. Accordingly, there is a need for a technique to correctly set exposure and color balance on the front end, i.e. prior to recording an image.
Obtaining correct exposure is part of the problem, the other part being correcting white balance. Most digital cameras provide different options for white balance correction which may be automatic or set by the photographer. Such settings are ballpark settings based on daylight, flash, overcast sky, tungsten filament lighting or fluorescent lighting. Daylight varies depending on the time of day with the color temperature being different at morning, midday and afternoon. There are also differences in white balance due to brightness of tungsten light bulbs because brightness determines color temperature. Since current white balance settings for digital cameras are quite inaccurate, there is a need for improvement.
In view of the aforementioned considerations, in digital photography there is need for improvement in the ability to select correct or desired exposure settings, as well as a need for improving the ability to correct or select desired white balance settings.